Cold email deliverability: domains, warm-up, SPF, DKIM and DMARC
Why your cold emails land in spam and how to fix it: dedicated domains, authentication, warm-up, volumes and Gmail and Yahoo sender rules.
The best email in the world is worthless if it lands in the spam folder. Deliverability, meaning your emails' ability to reach the inbox, comes down to a handful of technical rules and good sending habits. Here are the essentials.
Why your cold emails go to spam
Mailbox providers such as Gmail and Outlook score every sender. The signals that drag your reputation down:
- a new domain, or one with no history, that suddenly sends lots of email;
- missing or misconfigured authentication;
- a high bounce rate, a sign of a poor-quality list;
- recipients marking your emails as spam;
- content packed with links, images or pushy sales language.
Step 1: use dedicated sending domains
Never send outbound campaigns from your main domain, the one your invoices and customer emails go out from. Instead, buy one or more domains close to your brand (for example a .io or .co variant) that redirect to your website. If something goes wrong, only the sending domain is affected.
Step 2: authenticate every domain
Three DNS records prove you are the legitimate sender:
| Protocol | Role |
|---|---|
| SPF | Lists the servers allowed to send on behalf of your domain |
| DKIM | Signs every email to prove it has not been altered |
| DMARC | Tells receivers what to do with emails that fail the checks and sends you reports |
Since February 2024, Gmail's sender guidelines have required SPF or DKIM for all senders, and SPF, DKIM and DMARC (with domain alignment) for anyone sending more than 5,000 messages a day to Gmail. Yahoo applies similar requirements.
Step 3: warm up gradually
A new sending inbox has to build its reputation. Start with a few emails a day, then increase gradually over several weeks. During this period, favour conversations that generate replies. Warm-up tools automate this ramp-up, but they are no substitute for a good-quality list.
Step 4: keep volumes under control
- Spread sending across several inboxes and domains rather than pushing a single address.
- Stay at a few dozen emails per day per inbox.
- Spread sends through the day, during your recipients' office hours.
Step 5: look after your list and your content
- Verify addresses before sending to keep your bounce rate low.
- Monitor spam complaints: Gmail asks senders to stay below a 0.3% reported spam rate in Postmaster Tools.
- Write like a human: short text, few links, no attachments or images in the first email.
- Make it easy to unsubscribe: it is a legal requirement and it prevents complaints.
How to tell whether your emails are arriving
- Check Google Postmaster Tools to track your domain reputation and spam rate.
- Watch your reply rate: a sudden drop often points to a deliverability problem.
- Regularly test inbox placement on Gmail and Outlook mailboxes.
Open rates, on the other hand, are no longer a reliable indicator: some email clients open messages automatically.
What we handle for you
At Lead Matrix, sending domains, their authentication and their warm-up are included in the subscription, as are volume management and address verification. You focus on the replies. For the rest of the method, see our B2B cold email guide.
Frequently asked questions
How long does email warm-up take?
Usually several weeks, depending on the domain's history and the volume you are aiming for. A brand-new domain should not send large volumes on day one.
How many sending domains do I need?
It depends on your volume: several domains and inboxes let you spread sending and limit the risk.
Is DMARC mandatory?
For senders sending more than 5,000 messages a day to Gmail, yes. For everyone else, it is strongly recommended.
Can a blacklisted domain recover?
Often, by stopping sending, fixing the cause and resuming very gradually. Avoiding that risk is precisely why you should not use your main domain.